Many applications use an optical wavelength multiplexer to combine component light beams having mutually-different wavelengths into a single, multi-wavelength combined light beam. Such applications may additionally use, and other applications use an optical wavelength demultiplexer to divide a multi-wavelength combined light beam into its constituent component light beams having mutually-different wavelengths. Examples of such applications include optical communication systems and optical microscopy. Optical wavelength multiplexing and demultiplexing is optical multiplexing and demultiplexing based on wavelength rather than on some other optical property such as polarization state.
With many optical wavelength multiplexer and optical wavelength demultiplexer designs, the same optical device can be used to perform optical wavelength multiplexing or to perform optical wavelength demultiplexing simply by reversing the direction in which light travels through the device. Accordingly, as used in this disclosure, the term multiplexer encompasses a multiplexer and a demultiplexer, the exact function depending on the direction in which the light travels. Similarly, the term multiplexing encompasses multiplexing and demultiplexing, depending on the direction in which the light travels.
Lasers and LEDs are increasingly being used as light sources in a variety of epifluorescence and confocal fluorescence (including cytometry) applications. Light beams contributed by multiple discrete light sources in illumination subassemblies typically must be coaxial with arcsecond precision as they emerge from the multiplexer as a single combined beam prior to illuminating a test sample. In imaging subassemblies, light returning from the test sample is spectrally separated by an optical demultiplexer with similar precision requirements to ensure high measurement quantification and reproducibility when the separated component beams are detected.
In conventional optical wavelength multiplexers, at least some of the light beams subject to multiplexing pass through many beam-splitting surfaces, each of which has a transmission loss typically the range from 4% to 8%, although losses less than this can be obtained under carefully-controlled conditions. This results in a loss of optical intensity. For example, in a multiplexer that multiplexes eight component light beams, the intensity of some of the component light beams output by the multiplexer or demultiplexer is in the range from about 45% to 66% of the original intensity. In microscopy, each component light beam is subject to both multiplexing and demultiplexing, which multiples the intensity loss.
Accordingly, what is needed is an optical wavelength multiplexer/demultiplexer having lower optical losses than a conventional optical wavelength multiplexer/demultiplexer.